Agreed, wait a little longer. All springs especially soft springs settle over time. The few miles you have driven are not enough. Flexing them off road will make a big difference. On the other hand the rears are going to be settling too.

4runners are a lot heavier in the rear that trucks and most springs are made the same and to truck specs. I have learned to always go 1" more lift in the rear for my 4Runner and even that does not always do it. Oops, just re read your post, you already know this...

Do you have any old springs laying around? Could you just add an extra leaf to the rear and run it for a while? If you use a long leaf it probably won't be too stiff?